Reflex type loud-speaker



March 20, 1951 s. E. LEVY 2,545,961

REFLEX TYPE LOUD-SPEAKER Filed April 11, 194e FIG. 2.

Patented Mar. 20, 1951 UNI TEDVV PATEN T OFFICE REFLEX TYPE LOUD-SPEAKER Sidney Levy, Brooklyn, N. Y., assigner .toUniversity Loudspeakers, inc., White Plains,A N. Y., a ,corporationA of New York.-

Application April 11, 1946, Serial N0. 661,430

This vinvention has Yto do-With acousticdevices for reproducing `or receiving sound, particularly those capable of being used under adverse IWeather conditions as in outdoor `and `maritime `useror even under water.

WhenA used outdoors, these Vdevices arefexposed to moisture and to substances fcarried by fair and moisture. Particularly is this true in maritime work. When mounted on the deck-of avessel they maybe completelyv-engulfedby incoming` Waves and when mounted A.on a submersible oramphibious .craft .they may be vcompletely su'bmersed forlong periods. Under these conditions, Water will penetrate and/sometimes vll vthe sound passages .rand lsound:chamber. Aand come into contact withA the diaphragm. Salt'and 'other substances will deposit `on .the diaphragmand impair its operation. In additionv when lsubmersed to` any considerable depth the diaphragm lvvill 'be .sub-

jected to ,pressures greater thanzthie relatively light constructionof the1diaphrag=m willbear. Also; if the acousticdevicezzisgused on *,a warship or Vin theivicinity` of lheavyffordnancey Agun re or the concussion ,ofsexploding shells -Will :cause the alternate application of 'high-r andlow pressures n the diaphragm and this may-injure Athe diaphragm.

Known .formsof acoustic devices are unsuitable for useunder .adverse Weather conditions `or underwater. Thisispart-icularly true of thereiex type-horn loudspeaker or receiver, Which has the `advantage Vof compactness-but as lpresently designed hasthe disadvantage of having recesses and pockets Within vthe sound passages or chamber which trap water. Moreovernone of the present forms of reflex loudspeakers `are easily disassembled to permit either drainage of moisture .or cleaningbf the diaphragm. Usually it is necessary to disassemble the entire funit including `the diaphragmdriving'unit in Vorder to expose `the diaphragm. Also, existing means'for protectingv the ,diaphragm Vagainst high pressure or sudden variation in pressure such asvalvesin the soundpassages are 'unsuitableiforputdoor or under Wateruse since theytend to trap ;water.

The object of this. invention is to-overcome these deficiencies. .It provides an Aimproved form of .loudspeaker and receiverhaving agnovel sound chamber and Isound vpassage varrangement which results in greater compactness, permits moisturel to drain readily fromthe sound chamber and sound passages and in which the diaphragm can be-exposed for cleaning'by merelyremoving a cover. The ecoverserves .also tas a.;vvall =of the sound chamber and-sound .passage.'- Another `:fea-

21Claims. Cl. ISL- 31) ture of the invention is the provision of novel means 'for protecting the diaphragm from `injury caused by high pressure or sudden variation-*in pressure.

The preferred form ofthe invention is the special vform of reex type horn loudspeaker and receiver illustrated in the accompanying drawings, in which:

Fig. l is a side View in cross-section.

Fig. 2 is a partial side -view in cross-section `at the point Where a lead from they voice coil is attached to a terminal in the clamping ring.

The main structural units-are:

(a) the cylindrical-body IIJ With' an'inturned ange I I `at one end;

(b) the magnetic unit Within this' body for creating'the eld iiux. Any of 'the :known types of magnetic units providing an annular `air gap for a voice Coil may be used. Asshovvn the-magnetic unit consists of an annular permanent magnet 2l, a bottom plate l22, acentral core: 23 yand inner and outer pole pieces 25 and 26 formirrgan annular air gap 25 therebetween. The magnetic unit is supported by a vspider 2.1which is connected to the main body I lby screws28;

(c) the diaphragm having a stiffenedcentral portion 3i) which preferably is domeshaped and an annular ange 3| whichmayfbejprovided if desired vvvith annularscorrugations to .increase its flexibility. The edge ofthe annular v.iiange is clamped between clamping ring 32 ,and `annular pole piece l26;

(d) the voice Lcoil 4I] wound on an annular core which extendsfrom thediaphragm iiangel SI into the annular vairgap Y213 of the/magnetunit;

(e) the outer bell-shaped shell Elrforming a narrow annular, gradually expanding doublyreversed sound passage in conjunction `with the body Izand the inverted inner bell 5I, .theflatter being dome shaped atits innercentral part 52 to conform to the dome'of'the-diaphragm-andto forni .therewith a sound chamber; and

the dome shapedbuier 511iixedonthe central pole ,piece Atop or plate .25 with its Mouter surface near the diaphragm end, being of the same contour, serves to support thediaphragm when the diaphragm moves. invvardwbeyond its normalrange of vibration.

The cylindrical body `Ilis sealedat one end vby the diaphragm and at the other byithe base portion-ofouterbell 50. Watertightjoints fare obtained 'by' use of gaskets -I 2 and I3 between-clamping ring '32 and theinturned ange `I I :of-thefbody .Ie and .between the annular viiange -3l .of-thev diaphragm andannular pole Apiece26;of 4the magnetic unit and by gasket I4 between the lower edge of cylindrical body Ill and the base portion of outer shell 5G. The body Ill is attached to the outer bell 50 by any suitable means such as the screws I5. The leads from the voice coil pass between gasket I3 and the diaphragm flange 3l and are connected to terminals 33 anchored in recesses ed in the clamping ring 32 (see Fig. 2). Clamping ring 32 has a depending flange 34 which fits closely around the outside edge of the diaphragm and of thev annular top plate 26, and thus serves to position the voice coil accurately in the air gap. Notches or openings 35 are provided in flange 3d to permit wires from terminals 33 to pass down between the magnetic unit and body Iii to terminals 5t anchored in the base portion of outer bell 50.

The magnetic unit is thus enclosed in a watertight compartment, one wall of which is the diaphragm itself. It is therefore important that the diaphragm should be made of moisture resistant material or of material treated to resist moisture. Many plastics are suitable for this purpose. Preferably a thermo-plastic or thermo-setting plastic is used so that the diaphragm may be molded.

The inner bell 5I serves both as a cover for the diaphragm and as a wall of the sound chamber and sound passages. The bell 5I is spaced from the diaphragm by bosses 58 on the inturned flange II of the body I0. These bosses nest in recesses in the bell 5I. Screws 5B secure the bell 5I to the body I0. It will be noted that the bell 5I can be easily detached from the assembly by merely removing the screws 56. With the bell 5l removed, the diaphragm is exposed and can be cleaned.

The inner central portion of the bell 5I is shaped to conform to the central dome shaped portion of the diaphragm, and thus provides a dome shaped space between it and the diaphragm. This space is the sound chamber. The sound waves are mainly propagated by the dome shaped portion of the diaphragm. While the principal function of the annular flange is to support the dome shaped portion and to guide its movement, the annular flange also propagates sound waves to some extent but in diminishing degree from its inner circumference to the point where it is clamped by the ring 32. At a point about one half or two thirds of the distance outward from its inner circumference, the propagation of sound l waves becomes negligible, the exact point depending somewhat on the flexibility of the annular rim. It is desirable that the sound chamber be extended to embrace so much of the annular flange as effectively propagates sound waves. It is preferable therefore to have the central dome shaped portion of the inner bell 5I extend over a substantial portion of the annular flange 3|.

The exit to the sound chamber is between the lower edge 5l of the dome shaped portion of bell 5I and the annular ange SI. It will be noted that there is thus provided an annular exit along the entire circumference of the lower edge 5l of the dome shaped portion. Since the annular exit 'has a substantial radius, a comparatively large exit area is obtained with a narrow opening. With a centrallyA located opening or throat a much wider opening would be required to obtain the same exit area. A narrow opening from the sound chamber makes it possible to use a narrow sound passage. A narrow horn sound passage is desirable because frequency cancellation at bends is less in a narrow passage than in a wide one.

vWith a narrow passage sharper bends can be used and a more compact structure obtained.

An annular sound passage is provided in the space beyond the sound chamber between the ring 32 and body Il] and bell 5I and between the skirt of bell 5I and the skirt of bell 50. In the sound passage so formed, the direction of the sound wave is reversed twice between the exit from the sound chamber and the mouth of the horn. The ring 32, body I0 and bells 5I) and 5I are so disposed and shaped that the cross sectional area of the sound passage gradually increases from the sound chamber to the horn mouth in accordance with known horn design principles.

In this structure, when the loudspeaker is mounted with the axis a-a in a substantially horizontal position, any water or moisture penetrating the sound passage and sound chamber will drain freely therefrom. As appears from the drawing, the covered portion, i. e. the portion within the bell 5I, of the passage for sound waves through the sound chamber and sound passage proceeds along its entire length in a direction outward from the axis of the diaphragm, thus .permitting flow of liquid through this passage. There are no pockets or recesses to trap water.

In order to obtain high fidelity of reproduction, the diaphragm must be of relatively light construction. To protect the lightly consrtucted diaphragm from injury when it is subjected to high pressure a dome shaped buffer 66 is disposed within the dome shaped portion of the diaphragm. When the diaphragm is subjected to high pressure it will nest against and be supported by the buffer. The buffer should be separated from the diaphragm a distance in excess of the distance of maximum excursion of the diaphragm at peak audio power so as not to interfere with the sound propagating movement of the diaphragm. The buffer, however, should be near enough to the diaphragm to prevent the diaphragm from exceeding its maximum operative movement and by operative movement is meant the movement which the diaphragm can incur without injury. The buffer may be attached to the diaphragm diving mechanism by any suitable means such as a screw 6I coacting with a bracket 62 on the central top plate 26. A groove 63 may also be provided to receive the edge of the buffer and thus to assure that the buffer is properly centered under the diaphragm. It is desirable to provide openings in the buffer such as the slots t4 to minimize the damping effect of confined air between the buier and the diaphragm. Resilient means such as a rubber ring 65 may be provided to cushion the nesting of the diaphragm against the buffer 60 when the diaphragm is subjected to sudden pressure. When the loudspeaker and receiver is exposed to gunfire or to exploding shells the diaphragm is not only subjected to sudden pressure but also to sudden vacuum. The wave of compression is followed by a recession wave which sucks the diaphragm outward. In this event the diaphragm will nest in and be supported by the dome shaped portion of bell 5I. In order to perform this buffer function the dome shaped portion of bell 5I should be separated from the diaphragm an appropriate distance. In determining this distance the same considerations apply as those set forth with respect to the spacing of the buffer 6I) from the diaphragm.

What is claimed is:

1. In a reflex-type acoustic device suitable for marine use having a diaphragm, diaphragmdriving means and a longitudinal casing around said driving means with the diaphragm disposed in and sealing one opening thereof, the combination of a bell with its base disposed over the diaphragm to form a sound chamber with a narrow annular exit near the edge of the diaphragm, said bell having a :flaring skirt extending toward and around the casing, a second bell With its base closing the other opening in the casing opposite to that sealed by the diaphragm, terminals anchored in the base of said second bell and connected in the interior of the casing to the driving means, said second bell having a flaring skirt enwith bosses and recesses respectively in nesting relation so proportioned that when nested the base of said first bell will be properly spaced from the diaphragm and means for detachably securing said base of the first bell to the casing so that the diaphragm may be exposed for cleaning merely by removing said rst bell.

SIDNEY E. LEVY.

REFERENCES CITED The following references are of record in the ile of this patent:

UNITED STATES PATENTS Number Name Date 1,705,615 Cruber Mar. 19, 1929 1,727,105 Tflavvley Sept. 3, 1929 1,915,358 Giles June 27, 1933 1,917,007 Atkins July 4, 1933 2,058,555 Betts et al Oct. 27, 1936 2,194,070 Giannini Mar. 19, 19110 

